Recent studies of the trigeminal brain stem nuclear complex have served to reinforce the classic concept that orofacial nociceptive information is relayed to higher levels of the brain via the spinal trigeminal nucleus (STN). Although a great deal of information is available concerning the anatomy and connections of the STN, very little data is available regarding the neurochemistry or pharmacology of this system. The long term goal of the present proposal is to elucidate the chemical organization of the STN which underlies its pivotal role in nociceptive transmission through the use of anatomical, biochemical, pharmacological and electrophysiological techniques. This goal is defined by the following specific objectives: 1) To identify the neurotransmitters associated with trigeminal ganglion neurons that innervate the tooth pulp by employing double-labeling immunocytochemical methods in combination with retrograde labeling procedures; 2) To analyze the excitatory amino acid receptor subtypes associated with primary afferent synapses and trigeminothalamic neurons using in vitro receptor binding procedures after lesions of the trigeminal nerve or after injections of a retrogradely transported toxin into the thalamus; 3) To identify the transmitters associated with several key inputs to trigeminothalamic neurons by combining tract tracing procedures with immunocytochemistry; 4) To use in vivo microdialysis to analyze the release of substance P, adenosine and amino acid transmitters in the STN following tooth pulp electrical stimulation or veratridine stimulation of the STN. The location of chemically identified neurons contributing to transmitter release into the dialysate will be determined by administering a retrograde tracer directly into the dialysate and performing combined retrograde tracing immunocytochemical procedures. These studies will provide important new data concerning the chemical coded circuitry and pharmacology of the trigeminal system, toward the development of a better therapeutic approach to orofacial pain.